MRI/Ultrasound Fusion Imaging: The Future Is Now

Detecting possible prostate cancer

Magnetic Resonance Imaging (MRI) is changing the way prostate cancer is identified before a biopsy. Two technological improvements make it possible for MRI to detect suspicious areas in a prostate gland.

First, the new magnets are more powerful. The strength of a magnet is measured as Tesla, or T. Most radiology centers and hospitals used to have only 1.5T magnets. However, 3T magnets are now widely available, giving better image quality. Today’s 3T MRI clearly shows the anatomy of the prostate gland and surrounding structures.

Second, scanning adjustments and special software give particular information that identifies abnormal tissue in and around the prostate gland. Since tumor cells function differently than healthy cells, the software analyzes the image using different parameters; for this reason, it is called functional MRI or multiparametric MRI (mpMRI). The parameters can measure the presence of particular chemicals called metabolites; the flow of water molecules in the tissue; and the rate of uptake and washout of a contrast agent. When all this information is coordinated, 3T mpMRI tells us about the size, shape, location and aggressiveness of abnormal areas called suspicious lesions. This is called detection.

However, detection is not the same as diagnosis. MRI is not yet at a point where we can read a scan and say beyond a doubt that a suspicious lesion is or is not prostate cancer. The only way to do that is to use hollow biopsy needles to take tissue samples for examination under a microscope. Only then can a diagnosis of prostate cancer be made. The most accurate way to obtain the samples is by using advanced imaging called MRI/Ultrasound fusion to guide the biopsy needles into the target area.

What is MRI/Ultrasound fusion?

Fusion imaging, once a future dream, is finally here. It is a technological breakthrough that “marries” MRI images with real-time ultrasound. MRI uses magnetic energy and radiofrequency to capture images, whereas ultrasound uses sound waves (not detectable by the human ear) that bounce back, similar to the way sonar can find objects under water. MRI requires a very large, expensive piece of equipment used by imaging radiologists in special facilities, whereas ultrasound is small, inexpensive, and used every day by urologists in their own offices.

Before fusion came along, urologists performed ultrasound-guided biopsies to diagnose prostate cancer. However, ultrasound imaging does not reveal tissue differences within the prostate as well as mpMRI so ultrasound almost never shows tumors. The good news is that fusion imaging takes an MRI scan and merges it with the ultrasound images during the urologist’s scan. How does this work?

Co-registering images

Fusion technology uses complex computer algorithms to create an amazing “special effect.” By generating parallel coordinate systems between the MRI image and the real-time ultrasound, the computer combines the two images and has the elasticity to register them together, point by point. This generates a customized blended image of a patient’s prostate gland, and points to the suspicious lesion. The result looks like this:

IMAGE

Thus, an MRI scan is merged with real-time ultrasound while a patient is in the examining room.

Fusion-guided targeted biopsy

Until fusion, a typical ultrasound-guided biopsy involved taking an average of 10-14 needle samples from a systematic division of the prostate into 12 areas, six on each side of the gland. For the most part, this approach has been good at finding prostate cancer tumors, but sometimes it missed the cancer. The great advantage of fusion-guided biopsy is that the urologist can insert the biopsy needle precisely into the core of the suspicious lesion, and the ultrasound confirms that the needle reaches its target because the needle is visible on ultrasound. This accomplishes two important goals:

• It minimizes the number of needles taken, though most urologists will still sample a few other areas of the gland as a precaution
• It maximizes the accuracy of the diagnosis, because the center of the tumor is where the more dangerous cells are likely to be.

NOTE – If your urologist suspects you have prostate cancer, talk with him about having a 3T mpMRI before having a biopsy. The images obtained from the MRI are necessary to make fusion possible.

REMEMBER – The more accurate the biopsy, the earlier the diagnosis, the better you and your doctor can match treatment options, and the better the results of the therapy.